Citation or identification of any reference herein, or any section of this application shall not be construed as an admission that such reference is available as prior art to the present application.
There are three types of influenza viruses Influenza A, B, and C. Influenza types A or B viruses cause epidemics of disease almost every winter. In the United States, these winter influenza epidemics can cause illness in 10% to 20% of people and are associated with an average of 36,000 deaths and 114,000 hospitalizations per year. Influenza type C infections cause a mild respiratory illness and are not thought to cause epidemics. Influenza type A viruses are divided into subtypes based on two proteins on the surface of the virus. These proteins are termed hemagglutinin (H) and neuraminidase (N). Influenza A viruses are divided into subtypes based on these two proteins. There are 16 different hemagglutinin subtypes H1, H2, H3, H4, H6, H7, H8, H9 H10 H11 H12, H13, H14, H15 or H16 and 9 different neuraminidase subtypes N1 N2 N3 N4 N5 N6 N7 N8 or N9, all of which have been found among influenza A viruses in wild birds. Wild birds are the primary natural reservoir for all subtypes of influenza A viruses and are thought to be the source of influenza A viruses in all other animals. The current subtypes of influenza A viruses found in people are A(H1N1) and A(H3N2). Influenza B virus is not divided into subtypes.
In 1918, a new highly pathogenic influenza H1N1 pandemic swept the world, killing an estimated 20 and 50 million people. The H1N1 subtype circulated from 1918 until 1957 which then was replaced by viruses of the H2N2 subtype, which continued to circulate until 1968. Since 1968, H3N2 viruses have been found in the population. Because H1N1 viruses returned in 1977, two influenza A viruses are presently co-circulating (Palese and Garcia-Sarstre J. Clin. Invest., July 2002, Volume 110, Number 1, 9-13). The pathogenicity of the initial 1918 H1N1 has not been equaled by any of the latter H1N1, H2N2 or H3N2 subtypes, although infection from some subtypes can be severe and result in death. By molecular reconstruction, the genome of the 1918 flu including the amino acid sequences of the H1 and N1 antigens is now known (Kaiser, Science 310: 28-29, 2005; Tumpey et al., Science 310: 77-81, 2005).
In 1997, 2003, and again in 2004, antigenically-distinct avian H5N1 influenza viruses emerged as pandemic threats to human beings. During each of these outbreaks there was concern that the avian viruses would adapt to become transmissible from human to human. Furthermore, oseltamivir (Tamiflu®) was ineffective in 50% of avian influenza patients in Thailand (Tran et al. N. Engl. J. Med 350: 1179, 2004) and a new mutation in the neuraminidase has been identified which causes resistance to oseltamivir. Sequence analysis of the neuraminidase gene revealed the substitution of tyrosine for histidine at amino acid position 274 (H274Y), associated with high-level resistance to oseltamivir in influenza (N1) viruses (Gubareva et al., Selection of influenza virus mutants in experimentally infected volunteers treated with oseltamivir. J Infect Dis 2001; 183:523-531; de Jong et al., Oseltamivir Resistance during Treatment of Influenza A (H5N1) Infection. N. Engl. J. Med. 353:2667-2672, 2005). Such changes may alter the antigenic nature of the protein and reduce the effectiveness of vaccines not matched to the new variant. Other avian influenza strains of potential danger include H1N1, H7N7 and H9N2.
The optimum way of dealing with a human pandemic virus would be to provide a clinically approved well-matched vaccine (i.e., containing the hemagglutinin and/or neuraminidase antigens of the emerging human pandemic strain), but this cannot easily be achieved on an adequate timescale because of the time consuming method of conventional influenza vaccine production in chicken eggs.
2.1 Live Bacterial Vaccine Vectors
Live attenuated bacterial vaccine vectors offer an important alternative to conventional chicken egg based vaccines. Growth on embryonated hen eggs, followed by purification of viruses from allantoic fluid, is the method by which influenza virus has traditionally been grown for vaccine production. More recently, viruses have been grown on cultured cell lines, which avoids the need to prepare virus strains that are adapted to growth on eggs and avoids contamination of the final vaccine with egg proteins. However, because some of the vaccine virus may be produced in canine tumor cells (e.g., MDCK), there is concern for contamination of the vaccine by cancer causing elements. Moreover, both must undergo a labor intensive and technically challenging purification process, with a total production time of 3 to 6 months. Because of the time factors and scale-up, these vaccines are produced in large, but finite batches. Meeting a world-wide demand requires stockpiling of multiple batches. Therefore, traditionally produced vaccine produced before a pandemic, would likely be generated based upon an avian influenza virus and its antigens more than a year earlier and therefore may not be well matched to an emerging variant and could result in only partial protection. Bacterial vectors self replicate in simple growth media can be produced extremely rapidly by virtue of exponential growth and require minimal purification such as a single centrifugation and resuspension in a pharmaceutically acceptable excipient.
Human studies have shown that antibody titres against hemagglutinin of human influenza virus are correlated with protection (a serum sample hemagglutination-inhibition titre of about 30-40 gives around 50% protection from infection by a homologous virus) (Potter & Oxford (1979) Br Med Bull 35: 69-75). Antibody responses are typically measured by enzyme linked immunosorbent assay (ELISA), immunoblotting, hemagglutination inhibition, by microneutralisation, by single radial immunodiffusion (SRID), and/or by single radial hemolysis (SRH). These assay techniques are well known in the art.
Cellular responses to vaccination may also occur which participate in antiviral immunity. Cells of the immune system are commonly purified from blood, spleen or lymph nodes. Separate cell populations (lymphocytes, granulocytes and monocyte/macrophages and erythrocytes) are usually prepared by density gradient centrifugation through Ficoll-Hypaque or Percoll solutions. Separation is based on the buoyant density of each cell subpopulation at the given osmolality of the solution. Monocytes and neutrophils are also purified by selective adherence. If known subpopulations are to be isolated, for example CD4+ or CD8+ T cells, fluorescence activated cell sorting (FACS) will be employed or magnetic beads coated with specific anti-CD4 or anti-CD8 monoclonal antibody are used. The beads are mixed with peripheral blood leukocytes and only CD4+ or CD8+ cells will bind to the beads, which are then separated out from the non-specific cells with a magnet. Another method depends on killing the undesired populations with specific antibodies and complement. In some cases, a noncytotoxic antibody or other inhibitor can block the activity of a cell subtype. Characterization of cell types and subpopulations can be performed using markers such as specific enzymes, cell surface proteins detected by antibody binding, cell size or morphological identification. Purified or unseparated lymphocytes can be activated for proliferation and DNA synthesis is measured by 3H-thymidine incorporation. Other measures of activation such as cytokine production, expression of activation antigens, or increase in cell size are utilized. Activation is accomplished by incubating cells with nonspecific activators such as Concanavalin A, phytohemagglutinin (PHA), phorbol myristic acetate (PMA), an ionophore, an antibody to T cell receptors, or stimulation with specific antigen to which the cells are sensitized.
A key activity of cellular immunity reactions to pathogens such as viruses is the development of T lymphocytes that specifically kill target cells. These activated cells develop during in vivo exposure or by in vitro sensitization. The CTL assay consists of increasing number of sensitized lymphocytes cultured with a fixed number of target cells that have been prelabeled with 51Cr. To prelabel the target cells, the cells are incubated with the radiolabel. The 51Cr is taken up and reversibly binds to cytosolic proteins. When these target cells are incubated with sensitized lymphocytes, the target cells are killed and the 51Cr is released.
Natural killer (NK) cells are an essential defense in the early stage of the immune response to pathogens. NK cells are active in naïve individuals and their numbers can be enhanced in certain circumstances. The NK assay typically uses a 51Cr-labeled target and is similar to the CTL assay described above.
Specifically activated lymphocytes synthesize and secrete a number of distinctive cytokines. These are quantitated by various ELISA methods. Alternatively, induced cytokines are detected by fluorescence activated flow cytometry (FACS) using fluorescent antibodies that enter permeabilized cells. Activated cells also express new cell surface antigens where the number of cells is quantitated by immunofluorescent microscopy, flow cytometry, or ELISA. Unique cell surface receptors that distinguish cell populations are detected by similar immunochemical methods or by the binding of their specific labeled ligand.
Salmonella bacteria have been recognized as being particularly useful as live “host” vectors for orally administered vaccines because these bacteria are enteric organisms that, when ingested, can infect and persist in the gut (especially the intestines) of humans and animals.
As a variety of Salmonella bacteria are known to be highly virulent to most hosts, e.g., causing typhoid fever or severe diarrhea in humans and other mammals, the virulence of Salmonella bacterial strains toward an individual that is targeted to receive a vaccine composition must be attenuated. Attenuation of virulence of a bacterium is not restricted to the elimination or inhibition of any particular mechanism and may be obtained by mutation of one or more genes in the Salmonella genome (which may include chromosomal and non-chromosomal genetic material). Thus, an “attenuating mutation” may comprise a single site mutation or multiple mutations that may together provide a phenotype of attenuated virulence toward a particular host individual who is to receive a live vaccine composition for avian influenza. In recent years, a variety of bacteria and, particularly, serovars of Salmonella enterica, have been developed that are attenuated for pathogenic virulence in an individual (e.g., humans or other mammals), and thus proposed as useful for developing various live bacterial vaccines (see, e.g., U.S. Pat. Nos. 5,389,368; 5,468,485; 5,387,744; 5,424,065; Zhang-Barber et al., Vaccine, 17; 2538-2545 (1999); all expressly incorporated herein by reference). In the case of strains of Salmonella, mutations at a number of genetic loci have been shown to attenuate virulence including, but not limited to, the genetic loci phoP, phoQ, cdt, cya, crp, poxA, rpoS, htrA, nuoG, pmi, pabA, pts, damA, purA, purB, purI, zwf, aroA, aroC, gua, cadA, rfc, rjb, rfa, ompR, msbB and combinations thereof.
Bacterial flagella are known to be antigenic and subject to antigenic or phase variation which is believed to help a small portion of the bacteria in escaping the host immune response. The bacterial flagellar antigens are referred to as the H1 and H2 antigens. To avoid confusion with the viral hemagglutinin H antigen, the bacterial flagellar H antigen will be referred to as fH henceforth. Because the Salmonella-based vaccination of a heterologous antigen is dependent upon the bacteria's ability to colonize the gut, which may be reduced do to the initial immune response, the vaccination ability of the second immunization may be diminished due to an immune response to the vector. In Salmonella Hin invertase belongs to the recombinase family, which includes Gin invertase from phage Mu, Cin invertase from phage P1, and resolvases from Tn3 and the transposon (Glasgow et al. 1989, p. 637-659. In D. E. Berg, and M. M. Howe (ed.), Mobile DNA. American Society for Microbiology, Washington, D.C.). Hin promotes the inversion of a chromosomal DNA segment of 996 bp that is flanked by the 26-bp DNA sequences of hixL and hixR (Johnson and Simon. 1985. Cell 41:781-791). Hin-mediated DNA inversion in S. typhimurium leads to the alternative expression of the fH1 and fH2 flagellin genes known as phase variation. Hin (21 kDa) exists in solution as a homodimer and binds to hix sites as a dimer (Glasgow et al. 1989. J. Biol. Chem. 264:10072-10082). In addition to Hin and the two hix sites, a cis-acting DNA sequence (recombinational enhancer) and its binding protein (Fis, 11 KDa) are required for efficient inversion in vitro (Johnson et al. 1986. Cell 46:531-539). Live Salmonella vaccines have not had deletions of the hin gene nor defined fH1 or fH2 antigens, nor have they been constructed such that they lack fH antigens altogether. Accordingly, live Salmonella vaccines have not been constructed to maximize a prime-boost strategy which alternates or eliminates the fH antigen whereby the immune response of the fH antigen of the first immunization (prime) is not specific for the antigen of the second immunization (boost). Therefore, the boost immunization is not diminished by a rapid elimination by the immune system, and is therefore able to persist longer and more effectively present the immunizing antigen.
Introduction of viral genes into bacteria results in genetically engineered microorganisms (GEMs) for which there may be concern regarding containment of the introduced gene in the environment and its ability to reassort. Such genes could in theory provide virulence factors to non-pathogenic or less pathogenic viral strains if allowed to recombine under circumstances were the bacterial vaccine could co-occur at the same time in the same individual as a wild type viral infection. Thus, methods that reduce bacterial recombination and increase bacterial genetic isolation are desirable.
Insertion sequences (IS) are genetic elements that can insert copies of themselves into different sites in a genome. These elements can also mediate various chromosomal rearrangements, including inversions, deletions and fusion of circular DNA segments and alter the expression of adjacent genes. IS200 elements are found in most Salmonella species. S. typhimurium strain LT2 has six IS200s. Salmonella typhimurium strain 14028 has been described to possess an additional IS200 element at centisome 17.7 which is absent in other commonly studied Salmonella strains LT2 and SL1344 (Murray et al., 2004 Journal of Bacteriology, 186: 8516-8523). These authors describe a spontaneous hot spot (high frequency) deletion of the Cs 17.7 to Cs 19.9 region. Live Salmonella vaccines have not had deletions of IS200 elements which would limit such recombination events.
Salmonella strains are known to possess phage and prophage elements. Such phage are often capable of excision and infection of other susceptible strains and are further capable of transferring genes from one strain by a process known as transduction. Live Salmonella vaccines have not had deletions in phage elements such as phage recombinases which exist in Salmonella, such that the phage are no longer capable of excision and reinfection of other susceptible strains.
Salmonella strains are known to be capable of being infected by bacteria phage. Such phage have the potential to carry genetic elements from one Salmonella strain to another. Live Salmonella vaccines have not comprised mechanisms to limit phage infection such as the implantation and constitutive expression of the P22 phage repressor C2.
Bacterial expression of the viral hemagglutinin genes was first described by Heiland and Gething (Nature 292: 581-582, 1981) and Davis et al., (Proc. Natl. Acad. Sci. USA 78: 5376-5380). These authors suggest that the recombinant protein could be used as a vaccine without regard to the fact that the viral genetic loci are not optimal for bacterial expression. These authors did not suggest the use of live bacterial vectors as vaccine carriers, such as the genetically stabilized and isolated vectors of the present application, nor the use of defined flagellar antigens or no flagellar antigens. Nor did these authors suggest the use of secreted proteins.
Use of secreted proteins in live bacterial vectors has been demonstrated by several authors. Holland et al. (U.S. Pat. No. 5,143,830, expressly incorporated herein by reference) have illustrated the use of fusions with the C-terminal portion of the hemolysin A (hlyA) gene. When co-expressed in the presence of the hemolysin protein secretion channel (hlyBD) and a functional TolC, heterologous fusions are readily secreted from the bacteria. Similarly, Galen et al. (Infection and Immunity 2004 72: 7096-7106) have shown that a heterologous fusions to the ClyA are secreted and immunogenic. Other heterologous protein secretion systems include the use of the autotransporter family. For example, Veiga et al. (2003 Journal of Bacteriology 185: 5585-5590) demonstrated hybrid proteins containing the □-autotransporter domain of the immunoglogulin A (IgA) protease of Nisseria gonorrhea. Fusions to flagellar proteins have also been shown to be immunogenic. The antigen, a peptide, usually of 15 to 36 amino acids in length, is inserted into the central, hypervariable region of the FliC gene such as that from Salmonella muenchen (Verma et al. 1995 Vaccine 13: 235-24; Wu et al., 1989 Proc. Natl. Acad. Sci. USA 86: 4726-4730; Cuadro et al., 2004 Infect. Immun. 72: 2810-2816; Newton et al., 1995, Res. Microbiol. 146: 203-216, expressly incorporated by reference in their entirety herein). Antigenic peptides are selected by various methods, including epitope mapping (Joys and Schodel 1991. Infect. Immune. 59: 3330-3332; Hioe et al., 1990 J. Virol. 64: 6246-6251; Kaverin et al. 2002, J. Gen. Virol. 83: 2497-2505; Hulse et al. 2004, J. Virol. 78: 9954-9964; Kaverin et al. 2007, J. Virol. 81:12911-12917; Cookson and Bevan 1997, J. Immunol. 158: 4310-4319, expressly incorporated by reference in their entirety herein), T-cell epitope determination (Walden, 1996, Current Opinion in Immunology 8: 68-74) and computer programs such as Predict7 (Carmenes et al. 1989 Biochem. Biophys. Res. Comm 159: 687-693) Pepitope (Mayrose et al., 2007. Bioinformatics 23: 3244-3246). Multihybrid FliC insertions of up to 302 amino acids have also been prepared and shown to be antigenic (Tanskanen et al. 2000, Appl. Env. Microbiol. 66: 4152-4156, expressly incorporated by reference in its entirety herein) Modification of the fusion protein by inclusion of flanking cathepsin cleavage sites has been used to facilitate release within the endosomal compartment of antigen presenting cells (Verma et al. 1995 Vaccine 13: 235-244). Trimerization of antigens has been achieved using the T4 fibritin foldon trimerization sequence (Wei et al. 2008, J. Virology 82: 6200-6208, expressly incorporated by reference in its entirety herein).
Bacterial expression of the viral hemagglutinin genes was first described by Heiland and Gething (Nature 292: 581-582, 1981) and Davis et al., (Proc. Natl. Acad. Sci. USA 78: 5376-5380). These authors teach that the antigens may be purified from the bacteria in order to be used as vaccines and did not suggest the use of live attenuated bacterial vectors. Furthermore, the codon usage of the viral genome is not optimal for bacterial expression. Accordingly, a gram-negative bacterium of the enterobacteraceae such as E. coli and Salmonella will have a different codon usage preference (National Library of Medicine, National Center for Biotechnology Information, GenBank Release 150.0 [Nov. 25, 2005]) and would not be codon optimized. Further, these authors used antibiotic-containing plasmids and did not use stable chromosomal localization. Nor did these authors suggest heterologous fusions in order for the bacteria to secrete the antigens.
Kahn et al. (EP No. 0863211) have suggested use of a live bacterial vaccine with in vivo induction using the E. coli nitrite reductase promoter nirB. These authors further suggest that the antigenic determinant may be an antigenic sequence derived from a virus, including influenza virus. However, Khan et al. did not describe a vaccine for avian influenza virus. They did not describe the appropriate antigens for an avian influenza virus, the hemagglutinin and neuraminidase, and did not describe how to genetically match an emerging avian influenza virus. Furthermore, it has become apparent that certain assumptions, and experimental designs described by Khan et al. regarding live avian influenza vaccines would not be genetically isolated or have improved genetic stability in order to provide a live vaccine for avian influenza that would be acceptable for use in humans. For example, Khan et al. state that any of a variety of known strains of bacteria that have an attenuated virulence may be genetically engineered and employed as live bacterial carriers (bacterial vectors) that express antigen polypeptides to elicit an immune response including attenuated strains of S. typhimurium and, for use in humans, attenuated strains of S. typhi (i.e., S. enterica serovar Typhi). In support of such broad teaching, they point to the importance of “non-reverting” mutations, especially deletion mutations which provide the attenuation. However, non-reversion only refers to the particular gene mutated, and not to the genome per se with its variety of IS200, phage and prophage elements capable of a variety of genetic recombinations and/or even transductions to other bacterial strains. Khan et al. did not describe a bacterial strain with improved genetic stability, nor methods to reduce genetic recombination, such as deletion of the IS200 elements. Khan et al. did not describe a bacterial strain with improved genetic stability by deletion of the bacteria phage and prophage elements nor limiting their transducing capacity. Neither did Khan et al. describe methods to minimize bacterial genetic exchange, such as constitutive expression of the P22 C2 phage repressor.
The above comments illustrate that Khan et al. have not provided the field with an effective vaccine against avian influenza. Clearly, needs remain for a genetically isolated and genetically stable, orally administered vaccine against avian influenza which is capable of rapid genetically matching an emerging pathogenic variant.
Bermudes (WO/2008/039408), expressly incorporated herein in its entirety, describes live bacterial vaccines for viral infection prophylaxis or treatment. The bacteria described are live attenuated bacterial strains that express one or more immunogenic polypeptide antigens of a virus. The bacteria useful for the techniques described include Salmonella, Bordetella, Shigella, Yersenia, Citrobacter, Enterobacter, Klebsiella, Morganella, Proteus, Providencia, Serratia, Plesiomonas, and Aeromonas. Bermudes describes the serovars of Salmonella. enterica that may be used as the attenuated bacterium of the live vaccine compositions to include, without limitation, Salmonella enterica serovar Typhimurium (“S. typhimurium”), Salmonella montevideo, Salmonella enterica serovar Typhi (“S. typhi”), Salmonella enterica serovar Paratyphi B (“S. paratyphi 13”), Salmonella enterica serovar Paratyphi C (“S. paratyphi C”), Salmonella enterica serovar Hadar (“S. hadar”), Salmonella enterica serovar Enteriditis (“S. enteriditis”), Salmonella enterica serovar Kentucky (“S. kentucky”), Salmonella enterica serovar Infantis (“S. infantis”), Salmonella enterica serovar Pullorurn (“S. pullorum”), Salmonella enterica serovar Gallinarum (“S. gallinarum”), Salmonella enterica serovar Muenchen (“S. muenchen”), Salmonella enterica serovar Anaturn (“S. anatum”), Salmonella enterica serovar Dublin (“S. dublin”), Salmonella enterica serovar Derby (“S. derby”), Salmonella enterica serovar Choleraesuis var. kunzendorf (“S. cholerae kunzendorf”), and Salmonella enterica serovar minnesota (S. minnesota).
Bermudes describes attenuating mutations useful in the Salmonella bacterial strains which may include genetic locus selected from the group consisting of phoP, phoQ, edt, cya, crp, poxA, rpoS, htrA, nuoG, pmi, pabA, pts, damA, purA, purB, purI, zwf, purF, aroA, aroB, aroC, aroD, serC, gua, cadA, rfc, rjb, rfa, ompR, msbB and combinations thereof.
Although Bermudes discloses the msbB gene and the zwf gene, it was not recognized that in Salmonella, the deletion of the msbB gene confers sensitivity to carbon dioxide (CO2) and that deletion of zwf, a member of the pentose phosphate pathway (Fraenkel, D. G. 1996 Glycolysis, pp 189-198, In Eschericia coli and Salmonella typhimurium, F. C. Neidehardt (ed), ASM Press, Washington, D.C.), compensates for that deletion and restores resistance to carbon dioxide without losing the low degree of lipid A pyrogenicity (TNF-α induction) conferred by the msbB mutation. Furthermore, it was also not known that the msbB− Salmonella are also sensitive to acidic pH and osmolarity, and that the zwf mutation also enhances resistance to acidic pH and osmolarity. Therefore, the prior art does not teach a specific combination of these two mutations in order to obtain CO2 resistant bacteria. Nor would one ordinarily skilled in the arts be motivated to test for CO2 resistance in Salmonella deleted in msbB as there is no teaching that describes the occurrence of sensitivity or its importance. As described herein, CO2 and acidic pH-resistant ΔmsbB− bacteria have improved survival under physiological conditions advantageous for penetration into gut mucosal, lymphoidal and dendridic tissues at lower doses, in order to elicit an immune response to viral diseases.